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Nutritional management following bariatric surgery

Bariatric surgery is proving to be one of the most effective treatments for the morbidly obese patient. Nutritional requirements, before and after surgery, are discussed
Lisa Rickers
Bariatric Advanced Nurse Practitioner
Andrea Ralph
Senior Bariatric Dietitian
Oxford University Hospitals, Oxford, UK
Obesity levels continue to rise at an alarming rate and this now represents a global concern. The World Health Organization predicts that 700 million people will be obese by 2015, classified as a body mass index (BMI) of 30 kg/m2 or above.(1) The health consequences of being overweight are vast and are associated with an increased risk of type 2 diabetes, hypertension, cardiovascular disease, dyslipidaemia, arthritis, non-alcoholic steatohepatitis, sleep apnoea and several cancers.(2) In addition to these co-existing diseases, the psychosocial ramifications of being overweight and reduced quality of life are often under-reported within this population and tend to impact on women more than men.(3)
Bariatric surgery 
Bariatric surgery is proving to be one of the most effective treatments for the morbidly obese patient.(4) Indications for bariatric surgery are based on a number of criteria stipulated by the National Institute for Health and Care Excellence (NICE) Clinical Guideline 43:(5) 
  • The person has a BMI of 40kg/m2 or more, or between 35kg/m2 and 40kg/m2 and other significant disease (for example, type 2 diabetes or high blood pressure) that could be improved if they lost weight 
  • All appropriate non-surgical measures have been tried but have failed to achieve or maintain adequate, clinically beneficial weight loss for at least six months 
  • The person has been receiving or will receive intensive management in a specialist obesity service 
  • The person is generally fit for anaesthesia and surgery 
  • The person commits to the need for long-term follow-up. 
In addition, bariatric surgery is recommended as a first-line option (instead of lifestyle interventions or drug treatment) for adults with a BMI of >50 kg/m2 in whom surgical intervention is considered appropriate. Despite these guidelines commissioning teams within the UK often elevate BMI criteria in an attempt to reduce the number of referrals. 
A variety of surgical treatments exist and presently there are insufficient evidence-based data to suggest how to assign a patient to a specific bariatric procedure.(6) Common procedures include: 
  • Laparoscopic adjustable gastric band (LAGB)
  • Roux-en-Y gastric bypass (RYGB)
  • Sleeve gastrectomy (SG)
  • Biliopancreatic diversion with duodenal switch (BPD-DS.)
The mechanisms of action of these surgical procedures are often described as having a restrictive or malabsorptive component; however, as the knowledge around the pathophysiology of obesity improves, the role of gut hormones is thought to play an important role.(7)
More recently, there have been a number of clinical guidelines produced with recommendations for practice.(6,8) These are a welcome addition to this field to ensure the utilisation of evidence-based data, to promote excellence, to improve outcomes and to improve patient safety.
Pre-operative nutritional management
A common misconception is that obese patients meet their nutritional requirements by consuming an excess of calories. In reality, it is likely that nutritional deficiencies are prevalent within this group owing to food intake lacking in micronutrients, or increased nutritional requirements, and they often require supplementation of iron, vitamin B12 and vitamin D prior to surgery.(7) The effects of poor nutrition before surgery is not fully known but it seems sensible to treat these deficiencies particularly as further nutritional challenges are likely after surgery.
To date, there remains little guidance regarding the nutritional management prior to bariatric surgery and recommendations are variable between bariatric centres. It is common practice to recommend a pre-operative reduced calorie diet that promotes weight loss and reduces the size of the liver. This diet often promotes a restricted carbohydrate and calorie intake that reduces glycogen, water and fatty deposits in the liver, allowing the organ to be safely moved aside during the operation.(9) Patients should be advised against a large meal or last supper while on this diet as they risk reversing the reduction in liver size. In addition, diabetic patients who require insulin are likely to require instruction on dose adjustment, particularly if they are not used to carbohydrate counting. Glycaemic control often improves as a result of the reduction in carbohydrate content of this diet.(10)
Post-operative nutritional management
Little evidence exists regarding the progression of food textures following bariatric procedures and, as such, varying practices are in operation. Guidelines from the American Endocrine Society suggest the gradual progression of food textures over weeks to months in order to help minimise vomiting and potential damage to the surgical site.(11) From the authors’ experience, it is common that advice needs to be tailored to patients depending on the size of portions that are tolerated post-surgery.
Dumping syndrome can be experienced following a RYGB as a result of the pyloric sphincter being bypassed and undigested food being introduced to the small bowel. This can result in a number of unpleasant symptoms such as nausea, vomiting, bloating, cramping, diarrhoea, dizziness and fatigue, and is termed early dumping.(12) Late dumping can occur one to three hours following eating and patients may experience fluctuations in blood glucose levels, weakness, sweating, palpitations and dizziness.(13)
Dumping syndrome can be largely avoided if patients are able to make the appropriate changes to their eating habits and behaviours. These include avoiding food high in sugar or fat and promoting good eating techniques that help to avoid overeating.(12,13) Dumping is often viewed as a useful deterrent because of these unpleasant side effects; however, it is likely that this is short-lived and the incidence of dumping reduces over time.(14)
Macronutrient considerations
Maintaining protein requirements can be difficult after surgery, particularly with operations that have revised the small bowel, such as RYGB and BPD-DS. Protein is essential for growth and maintenance of body tissues as well as playing a key role in enzyme, transport, hormone, immune and blood buffering functions. General guidelines suggest that 60g protein are required in order to minimise malnutrition but due to the development of intolerances to protein-rich foods, this can be difficult to achieve in the short term.(14) Education about eating behaviours, such as taking small mouthfuls, chewing well and alternative sources of protein, is key to maintaining adequate intakes.
Micronutrient considerations
Micronutrient intakes will be reduced as a result of limited portion sizes and the primary focus on protein-containing foods post-operatively. In addition, absorption of micronutrients may be affected by more rapid gut transit as seen in RYGB and BPD-DS. 
Vitamin and mineral deficiencies are common to all bariatric procedures; however, some procedures are more likely to result in specific nutrient deficiencies, as outlined below. A combination of poor eating behaviour, low intake of nutrient dense foods, small portion size and intolerance of certain foods can contribute to micronutrient deficiencies. Common deficiencies after surgery include calcium and vitamin D, iron, thiamine, vitamin B12 and zinc.(7) Table 1 outlines the common deficiencies and the micronutrient considerations linked to specific bariatric surgical procedures.
Further considerations for patients who have undergone BPD-DS
In addition to the deficiencies described, the following micronutrients should be considered due to altered fat absorption caused by resection of the intestine:(7)
  • Vitamin K, which plays a key role in blood clotting
  • Vitamin A, which is required for normal tissue development, deficiency affects rapid turnover tissues such as the skin and eyes.
Biochemical monitoring and supplementation
Monitoring and supplementation of micronutrient levels pre- and post-surgery are essential to ensure the patient is in the optimum condition for surgery (as previously discussed) and to reduce the consequence of micronutrient deficiencies after surgery. Table 2 is for guidance only and more frequent monitoring may be required depending on the patient’s condition or clinical concerns, for example, a change in patient’s health, persistent vomiting or deficiency symptoms suspected.
Routine micronutrient supplementation
During the pre-op diet, it is suggested to commence a complete multivitamin and mineral supplement because it is likely that nutritional intake will be reduced. Following surgery, all patients will initially follow a liquid diet and will need to take a liquid or chewable multivitamin and mineral supplement until they are able to tolerate solid textures. These preparations are only recommended in the short-term because they are often not complete in vitamins and minerals. Once the patient is established on normal textured food they should be encouraged to return to a complete multivitamin and mineral supplement tablet.
Patients who have undergone a RYGB, GS or BPD-DS are recommended a three-monthly vitamin B12 injection for the first year; following this, requirements should be based around individual biochemistry results, and for some patients can be reduced to six-monthly intervals. If vitamin B12 remains at the lower end of normal, ongoing three-monthly injections will be required. Vitamin B12 injections are required lifelong, and it is imperative that patients are made aware of this to ensure they can make informed decisions.(20)
Calcium and vitamin D preparations will need to be considered for patients post-RYGB, SG and BPD-DS. Some patients following insertion of a LAGB may also require supplementation, depending on their biochemistry levels.(21) Preparations recommended within the UK are chewable and provide both the active form of vitamin D (colecalciferol) and calcium (calcium carbonate). The dose of supplementation should be tailored to the patient’s individual needs and monitored as recommended.
Menstruating women may require iron supplementation in addition to their multivitamin and mineral tablet as a result of the reduced intake in iron-rich foods.(18)
From the authors’ experience, the following factors can help enable patients to optimise their success and attain their goals following bariatric surgery:
  • Regular activity including structured activity and incidental activity. Choosing activities that are enjoyable and achievable will help improve adherence
  • Attendance at social support networks, including patient support groups can provide additional motivation and to share successes and address common obstacles
  • Commitment to long-term follow up to ensure nutritional adequacy of the diet will help to optimise patient goals and reduce complications and nutritional deficiencies
  • The acquisition of appropriate coping strategies as opposed to using food
  • The adoption of healthier habits and hobbies to promote a healthy active lifestyle will enable sustained results and help avoid weight regain.
  1. World Health Organization. Obesity: Preventing and Managing the Global Epidemic. Report of a WHO consultation. Geneva:Who Technical Series;2000.
  2. Haslam DW, James WPT. Obesity. Lancet 2005;366:1197–209.
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  5. National Institute of Clinical Health and Excellence. Obesity (CG43): Guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children. London:NICE;2006. 
  6. Fried M et al. Interdisiplinary European guidelines on surgery of severe obesity. Obesity Facts 2008;1:52–9.
  7. Aills L et al. ASMBS allied health nutritional guidelines for the surgical weight loss patient. Surg Obesity Rel Dis 2008;4:S73–S108.
  8. National Confidential Enquiry in Patient Outcomes and Deaths (NCEPOD) Too lean a Service? A review of the care of patients who underwent bariatric surgery;2012. (accessed 3 December 2012).
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  10. Dyson PA. A review of low and reduced carbohydrate diets and weight loss in type 2 diabetes. J Hum Nutr Diabet 2008;21: 530-8.
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  12. Ukleja A. Dumping syndrome: pathophysiology and treatment. Nutr Clin Pract 2005;20(5):517–25.
  13. Tack J et al. Pathophysiology, diagnosis and management of post-operative dumping syndrome: symptoms. Nat Rev Gastroenterol Hepatol 2009;6:583–90.
  14. Bock MA. Roux-en Y gastric bypass: the dietitian’s and patient’s perspectives. Nutr Clin Pract 2003;18(2):141–4.
  15. Thomas B. The Manual of Dietetic Practice, Fourth Edition. 2007. Blackwell Publishing
  16. Williams SE. Metabolic bone disease in the bariatric surgery patient. J Obesity 2011; Article ID 634614.
  17. Scientific Advisory Committee on Nutrition. Iron and health. The Stationery Office;2010:London. 
  18. Mechanick JI et al. American Association of Clinical Endocrinologists, The Obesity Society, and American Society for Metabolic & Bariatric Surgery Medical Guidelines for clinical practice for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric surgery patient. Surg Obesity Rel Dis 2008;4(5 Suppl):S109–S184.
  19. Scientific Advisory Committee on Nutrition. Folate and disease prevention. The Stationery Office;2006:London.
  20. Smith CD et al. Gastric acid secretion and vitamin B12 absorption after vertical Roux-en-Y gastric bypass for morbid obesity. Ann Surg 1993;218:91–6.
  21. Pearce SH, Cheetham TD. Diagnosis and management of vitamin D deficiency. Br Med J 2010;340:142–7.